dry yeast rehydrated in wort culprit of high FG?

[tomaso]

I've been struggling with my beers finishing a bit high (about 4-5 points) for a while now and I thought that I'd narrowed it down to the mash temp being too high due to taking the temp in the middle of the pot (BIAB) instead of the bottom where the grain is closest to the still warm stove. Does that make sense?

But I just recently learned about my mistake of rehydrating dry yeast in extract instead of water (After 40 batches!) and am wondering now whether that could be the problem... guess I'll see anyway now after doing it properly but was just wondering whether dry yeast rehydrated in extract could be suffering so much as to reduce it's viability/cell count to the point that even a whole 10g envelope of Safale rehydrated in extract and pitched into 3 Gallons of average gravity wort wouldn't ferment out....

Thx

 

[Legume]

It is unlikely that rehydrating in wort of any reasonable gravity would cause a high FG, especially if you are using 1 packet of yeast to 3 gal of wort (over pitching).

Many people do not bother to rehydrate dry yeast...they just dump it into the cooled wort. I have done this many times without underattenuation problems.

Out of curiosity, what yeast(s) are you using?

You are probably right to focus on your mash temps.

 

[Gavin C]

If you are worried about the viability of the dry yeast you should look into rehydrating it as per the designers instructions.

What you are describing though is likely to be tied to mash temperature. An accurate thermometer and fast dough in are useful with BIAB.

The other culprit could be recipe. Can you post an example. High percentages of specialty unfermentable grains would be something to look at.

 

[kh54s10]

I would say that rehydrating in wort would more likely lead to off flavors than under attenuation. The yeast will be alive but stressed and will have to work harder to reproduce leading to longer time until they are fully working at fermenting the wort.

It is likely a combination of things. Stir the mash very well then take your temperature readings. Check your thermometers. Make sure your recipes don't contain too much in the way of unfermentables.

If you do a batch with yeast rehydrated in water and your problem goes away you will know. Or if it is still under attenuated you have eliminated one possibility.

 

[SteveH aka shetc]

I use wort to rehydrate Safale US -05 all the time. From the Fermentis instructions : "Sprinkle the yeast in minimum 10 times its weight of sterile water or wort at 27°c ± 3°C (80°F ± 6°F)."

 

[tomaso]

Thanks for all your replies.
I also think that it's more likely related to mash temp than to the yeast... and it is weird, as shetc said, that fermentis says you can rehydrate it in wort or water... which I think is why I did that in the first place (already completely had forgotten about that) but then I read the sticky in the yeast forum which advised against it.... can someone comment on that???

I'll take more care with the mash temp measuring the next batches and report back.

It's not the recipes, it happens as well with recipes from other people which are tried and tested

 

[IslandLizard]

Aside from re-hydration in plain water, NOT distilled/RO water, the yeast needs some minerals and ions, good aeration/oxygenation of the wort at pitching time may help to attenuate more. So does raising the temps toward the end of the fermentation. You're not using a secondary are you? That can be another reason for stalling short of calculated FG.

 

[Owly055]

Aside from re-hydration in plain water, NOT distilled/RO water, the yeast needs some minerals and ions, good aeration/oxygenation of the wort at pitching time may help to attenuate more. So does raising the temps toward the end of the fermentation. You're not using a secondary are you? That can be another reason for stalling short of calculated FG.

The type of water (distilled, RO, or decent quality tap) used for rehdration is not relevant so long as it is sterile........ Rehydration is the only thing the water is used for. Rehydration is a matter of miniutes, not days. The purpose of rehydrating in water is osmosis. Wort exerts an osmotic pressure on the yeast cells that inhibits the uptake of water for hydration. The yeast packet contains everything the yeast needs in terms of minerals, etc to get started. Well aerated wort has everything else........... I personally don't go to a lot of trouble with aeration normally. Simply pouring into the fermenter in a way that creates lots of aeration seems to work well for me. I've used a paint stirrer to whirlpool it and further aerate it, and come to the conclusion that it's a waste of time..... the resulting beer is not noticeably better or worse. Most dry yeast is pretty darn bullet proof it would seem. I've used Fermentis, Danstar, and Muntons, all with excellent results. At least one study has shown that rehydrating in COOL water.... I forget the actual temp but believe around 60F produces the best live cell count...... about double that of rehydrating in wort. These yeast packets contain a LOT of cells...... a good pitch for a 5 gallon brew just sprinkling it on the wort.

Personally I would suspect mash temperature...... OR hydrometer reading..... Under pitching will take longer to start, and longer to attenuate....not under attenuate.


H.W.

 

[SteveH aka shetc]

I'll write to Fermentis and ask them to fix their instructions.

 

[Owly055]

I'll write to Fermentis and ask them to fix their instructions.

Do that please....... It will save me the trouble ;-) There are a number of studies out there, all of which recommend plain water for rehydrating...... Temperature is a point of contention. I lean toward the cooler numbers simply because you are ONLY trying to rehydrate.....nothing more. In terms of osmotic pressure, distilled water should be the best medium for rehydration. But that's a bit extreme. My well water is superb........ I'm not going to hook up my water still just to rehydrate yeast.


H.W.

 

[tomaso]

Maybe a bit off thread but then my question here is why does fermentis recommend to rehydrate in water/wort of 27C if we ferment much lower?? And when we pitch that 27C rehydrated yeast into wort chilled down to our 20C ferm temp does that shock the yeast?

That's what I do here in BArcelona at the moment where ambient temps are around 28C. I pitch into 23C wort and then put the carboy in my chest freezer which is set at 20C but maybe it's better to keep it all at the same temp, i.e. rehydrate in 20C water, pitch it into 20C wort and put that into the 20C ferment chamber...?

 

[dstar26t]

http://seanterrill.com/2011/04/01/dry-yeast-viability/

 

[Firewalker11]

If you are worried about the viability of the dry yeast you should look into rehydrating it as per the designers instructions.

Balls!